First Prior Art
Widely used conventional liquid crystal display devices display images by combining twisted nematic liquid crystal and a polarizing plate so as to control penetrating light for each pixel. Conventional liquid crystal display devices for displaying color images have micro color filters corresponding to adjacent three pixels and penetrating red, green, and blue lights by the additive process.
However, in such a conventional liquid crystal display device a large amount of light absorption in the polarizing plate and the micro color filters causes the transmissivity in the entire liquid crystal display device to be about 10% or less, making it difficult to provide bright display images. In particular, in a reflective type liquid crystal display device which utilizes external light, the display is likely to be so dark as to make the colors unrecognizable.
Japanese Laid-open Patent Applications No. 61-238024 and No. 3-238424 show liquid crystal display devices which display bright color images even when they are used as reflective type because of a guest host mode for controlling the absorption and penetration of light for each color by using dichroic dyes. These liquid crystal display devices comprise a plurality of stacked panels each having a liquid crystal layer containing a dichroic dye different from each other. To be more specific, the three liquid crystal panels each comprise liquid crystal containing dichroic dyes of cyan, magenta, or yellow and sealed into between a pair of glass substrates. When all the panels absorb light, images are displayed in black; when all the panels penetrate light, images are displayed in white; and when one or two panels absorb light, images are displayed in colors. Not having a color filter or a polarizing plate for absorbing light, the display device with the guest host mode provides bright and clear color display and is suitable for a reflective type liquid crystal display device.
However, the liquid crystal display device comprising a plurality of stacked panels each having a pair of glass substrates has the following drawback. When the pixels are small, the thickness of the glass substrates composing each panel becomes relatively large as compared with the size of the pixels, and as a result, the parallax becomes so influential as to cause unevenness in color when display images are seen in a diagonal direction.
In order to solve the unevenness in color due to the parallax, a so-called polymer diffusion type liquid crystal display device has been proposed as in Japanese Laid-open Patent Application No. 6-337643. FIG. 79 shows the polymer diffusion type liquid crystal display device, which comprises a substrate 1291 and liquid crystal layers 1295-1297 stacked thereonto by solidifying a resist material or polymeric material 1298 in which a guest host liquid crystal 1299 is dispersedly held. The display device further comprises driving electrodes 1292-1294 which correspond to the liquid crystal layers 1295-1297, respectively and are connected with corresponding driving elements formed on the substrate 1291. Such a structure requiring no glass substrate between adjacent ones of the liquid crystal layers 1295-1297 realizes a liquid crystal display device with a guest host mode which is freed of unevenness in color resulting from parallax.
However, in the polymer diffusion type liquid crystal display device, the guest host liquid crystal 1299 is dispersedly held in the resist material or polymeric material 1298, so that the resist material or polymeric material 1298 makes up a large proportion of the liquid crystal layers 1295-1297 (the guest host liquid crystal 1299 makes up a small proportion of the liquid crystal layers 1295-1297). This causes a problem that a substantial open area ratio becomes small, making it difficult to have a high contrast ratio.
Prior to the liquid crystal display device of the present invention, the inventors of the present invention have proposed a liquid crystal display device in Japanese Laid-open Patent Application No. 9-127057 which is shown in FIG. 80. The liquid crystal display device comprises a substrate 1101, film-like sealing plates 1113-1115 stacked on the substrate 1101 while being supported by supporting members (spacers) 1108-1110, and liquid crystals 1125-1127 sealed into between the substrate 1101 and the sealing plate 1113, between the sealing plates 1113-1114, and between the sealing plates 1114-1115, respectively. The use of the film-like sealing plates 1113-1115 supported by the supporting members 1108-1110 solves the unevenness in color due to parallax which is caused when glass substrates are used. Furthermore, the polymeric material which is used to hold liquid crystal in the above-mentioned polymer diffusion type liquid crystal display device is not required, so that the liquid crystal makes up a large proportion of the liquid crystal layers 1125-1127 disposed between adjacent ones of the sealing plates 1113-1115. This makes it possible to increase a substantial open area ratio, thereby increasing the contrast ratio.
The supporting members 1108-1110 can be formed by applying a photosensitive resin onto each of the substrate 1101 and the sealing plates 1113 and 1114 and polymerizing and hardening parts of the photosensitive resin by mask exposure, where the supporting members 1108-1110 are formed, and then eliminating the remaining part of the photosensitive resin by development.
However, in the liquid crystal display device comprising the stacked film-like sealing plates 1113-1115, each of the supporting members 1108-1110 must be formed exactly in the same position as each other in order to securely support the sealing plates 1113-1115. For example, when the supporting members 1108 are formed in different positions from the supporting members 1109 as shown in FIG. 81(a) due to low precision in positioning, these sealing plates are deformed as shown in FIG. 81(b) by the pressure of bonding the sealing plate 1114 to the substrate 1101. When the positional deviation between the supporting members 1108 and 1109 is large, the supporting member 1109 of a second display layer 1122 encroaches on a first display layer 1117 as shown in FIG. 81(c) so as to destroy the first and second display layers 1117 and 1118. In order to avoid this problem, the formation of the supporting members 1108-1110 by mask exposure requires mask alignment of high precision.
Since the supporting members 1108 and 1109 are in the region where the light transmissivity is not controlled, it is preferable to make the area for the supporting members 1108-1110 in pixels as small as possible in order to have a larger open area ratio. This requires higher precision in mask alignment. To be more specific, in the case where the supporting members 1109 are square pillars of 7 .mu.m.times.7 .mu.m, the positional deviation of 3 .mu.m or more between the supporting members 1108 and 1109 damages the first display layer 1117 and other components as described above. Therefore, mask alignment must be performed so as to make the positional deviation less than 3 .mu.m.
As a result, the device has a problem that the provision of a precision masking process leads to an increase in the production cost.